Planets: Romulus and Remus (aka Romii).

Until stardate 1709.2 when the U.S.S. Enterprise NCC-1701 under the command of Captain James T. Kirk had an unfriendly run-in with a Romulan ship. Very little was known about the species in general, although theories did exist. Although descended from the same ancestors as are Vulcans, the Romulans are surprisingly different from their distant cousins both in physiology and in behavioral customs. Romulan technology includes the "cloaking device" allowing them stealth and making them formidable opponents.

The physiology is subtly different from Vulcans, but enough so that surgery on a severely injured Romulan is difficult for Dr. Crusher. Romulan ribosomes apparently do not match those of humans or, surprisingly, Vulcans — but can match those of Klingons. The race still believes in discarding genetically or physically inferior infants, and that it will conquer the galaxy. They view the Federation as exploitative and short-sighted, according to Jarok. Their metabolism — or at least his — appears to be faster than human standard; the higher rate will help his treated skin burns heal faster. Throughout their long history of war, Romulans have rarely attacked first, opting instead to test their enemies' resolve — a chess game, Captain Picard calls it.

A very moral people with an absolute sense of right and wrong, enemy and friend — a purposeful, passionate commitment a young Ensign DeSeve found attractive when he defected but lost faith with over time. Many ordinary Romulans, even those in the military, have horror stories about treatment by the Tal Shiar — a military service which appears to operate above the standard empire. Natives learn quickly to be secretive and not to volunteer information. Women as well as men can climb high in both the military and the Tal Shiar, as evidenced with Deanna Troi's capture on stardate 46519.1 in which she posed as a Romulan from the Tal Shiar successfully. Its leaders had no information about Klingon dishonor in being captured, so Tokath thought he was being kind in letting the Khitomer survivors be kept alive. A Romulan ship was shadowing the competing Cardassians, Starfleet and Klingons all along in the race for the last clues in Galen's ancient DNA puzzle.

The Romulans' preference for waiting and observing while other make the first move would explain why they have never ventured into the Gamma Quadrant.

The species is made up of many varied skin tones, from a yellow tinged to a dark brown.

As a rule, they claim to have invented every technological breakthrough before any other culture.